I have a 2004 Mazda 6 and really love my car. Its paid for; therefore I want to keep it as long as possible. My car began to jerk randomly sometimes when I increase speed and is sometimes slow to take off. My CEL is on and Ive taken it to Advance Auto and got the following codes: P0301, P0306, P0443 and P0421. I understand that the first two are misfires and have ordered coil packs for those two cylinders. However, the other two codes Im not sure what I should get checked or replace. Any ideas? Please help! Thanks.